Treated cotton could help irrigate deserts

Researchers have developed a special treatment for cotton fabric that allows it to absorb large amounts of water from misty air and release it by itself as it warms.

Fine-mesh fog harvesting nets are already used in some mountainous and coastal areas. But these collect water from misty air, with droplets forming on the nets and falling to the ground, and depend on a good strong wind.

The new coated cotton, though, can work in still air; and, says the team, can be laid directly where the water is needed, for example on cultivated soil.

One big advantage is that the basic material – cotton fabric – is cheap and can be easily produced locally. The polymer coating increases the cost slightly, but only by about 12 percent, says the team.

The Eindhoven University of Technology and Hong Kong Polytechnic University researchers use a coating of PNIPAAm, a polymer, on the fabric. At lower temperatures, this has a sponge-like structure at microscopic level, and can absorb 340 percent of its own weight of water from misty air.

Once the temperature goes up, though, the material becomes hydrophobic or water-repellant, and above 34°C its structure is completely closed. It then releases all the absorbed water, in a cycle that can be repeated many times.

The material could potentially provide water in deserts or mountain regions, where the air is often misty at night. But the team's also looking at completely different applications such as tents that collect water at night, or sportswear that keeps perspiring athletes dry.